1. Field of the Invention
This invention lies in the field of ultraviolet radiation absorbers and particularly involves the use of certain pthalisoimides as substrate protectants for ultraviolet radiation.
2. Prior Art
It is known that light, in particular, ultraviolet (UV) radiation, causes the breakdown of various manufactured substances, such as synthetic polymers, natural fibers, and the like. UV radiation also damages human skin and hair. UV radiation in wavelengths ranging between about 290 and 320 nanometers (nm), is sometimes called UV-B radiation, and that between about 320 and 400 nm is sometimes called UV-A radiation.
UV-B radiation from the sun reportedly causes almost all of the photobiological skin reactions, including erythema, edema, blistering, and skin cancer. The longer UV-A rays produce minor photobiological reactions, such as immediate tanning and immediate transient erythema responses. Together, UV-A and UV-B radiation are responsible for the majority of photoinjuries to the skin.
Therefore, broad spectrum ultraviolet radiation absorbers are needed to protect both manufactured products (such as polymers, fabrics, and the like) and natural products (such as human skin and hair), from the damaging effects of UV radiation. For manufactured products, this can be accomplished by either coating the product, or incorporating into the product (especially surface regions), a UV absorber or mixture of UV absorbers. Broad formulation compatibility is desirable. For protecting natural surfaces, sunscreen compositions that incorporate UV absorbers or mixtures of UV absorbers are applied topically, and UV absorbers so incorporated must additionally be nontoxic to mammals (including man). UV absorbers which are relatively inexpensive to produce are desirable.
Broad spectrum screening of ultraviolet radiation in sunscreen compositions is generally accomplished by two techniques. In one technique, a UV-B absorber is admixed with a UV-A absorber and the mix is blended into a suitable cosmetic carrier. This technique is usually expensive because of the high cost of each absorber.
In the second technique, a single compound that absorbs both UV-A and UV-B radiation is blended into a suitable cosmetic carrier. An example of a prior art compound employed in practicing this second technique is a benzalphthalide of the type taught in U.S. Pat. No. 4,333,920, issued June 8, 1982 which discloses such benzalphthalides to be effective as broad spectrum sunscreens that absorb UV radiation over the range from about 290 nm to 350 nm. However, benzalphthalides suffer from the problems associated with other prior art broad spectrum UV absorbers or screens, which are: high manufacturing costs, low product yield, and, therefore, high cost of final product.
A practical broad spectrum UV absorber should protect manufactured products and/or human skin and hair from the harmful effects of the UV-A and UV-B radiation, and also be resistant to oxidation and photodegradation under all storage and application conditions. It is desirable that the UV absorber be economical to produce. Also, a broad spectrum UV absorber for cosmetic use should be substantially oil-miscible or capable of forming a non-granular smooth suspension in conventional cosmetic oil carriers suitable for use in sunscreen compositions. Further, such broad spectrum UV absorber should be effective, substantially nontoxic, and cosmetically acceptable under normal use conditions. Still further, such a UV absorber for use in protecting manufactured products should be compatible with the other agents commonly used in such products. The art needs new and improved broad spectrum UV absorbers having a combination of such properties.